In recent years there has been significant progress in the development of pressure compensated directional control valve assemblies for fluid control systems. U.S. Pat. No. 3,693,506 discloses a control circuit for a plurality of manual control valves, each controlling a fluid motor. The control circuit includes a logic system for sensing each load-actuating pressure, and for selecting the highest pressure sensed and directing this pressure to actuate means for controlling a source of supply pressure. U.S. Pat. No. 3,592,216 discloses a flow control valve for use with such a control circuit. The flow control valve limits the pressure supplied to the manual control valves and maintains the required fluid flow thereto. U.S. Pat. No. 3,631,890 discloses a flow-extending bypass valve which may be used with the control circuit. The flow-extending bypass valve adjusts automatically to bypass fluid at an increased differential pressure when a fluid motor is actuated, thereby extending the flow capacity of the manual control valve associated with the fluid motor.
There remains a need in the art for a directional control valve assembly having a manual control valve movable to a float position, and having motor port lock-out valves actuated automatically when the manual control valve is moved to the float position. Such automatic acutation should take place at a pressure well below load-actuating pressure. When the directional control valve assembly incorporates a plurality of manual control valves, or when a plurality of assemblies are incorporated in the fluid control system, the motor port lock-out valves should remain open while their associated manual control valve is in the float position, and still allow operation of any of the remaining manual control valves in the power positions.